Negative resist composition and pattern forming process

ABSTRACT

A negative resist composition comprising a polymer comprising recurring units (a) of formula (1) and having a Mw of 1,000-500,000 as base resin is provided. R 1  is H or methyl, X is a single bond or —C(═O)—O—R 4 —, R 2  is a single bond or C 1 -C 4  alkylene, R 3  is C 2 -C 8  alkylene, R 4  is a single bond or C 1 -C 4  alkylene, and 0&lt;a≦1.0. The composition exhibits a high resolution due to controlled acid diffusion and forms a resist film which is unsusceptible to swell in the developer and hence to pattern collapse.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2013-245671 filed in Japan on Nov. 28, 2013, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a negative resist composition, more particularly to a chemically amplified negative resist composition comprising a specific polymer, and a pattern forming process.

BACKGROUND ART

To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, a self-aligned double patterning (SADP) process involving the steps of forming a resist pattern by ArF lithography, growing a film on opposite sides of pattern features, and forming two pattern features with a half line width from one resist pattern feature is utilized to manufacture 20-nm node devices on a mass scale. One candidate for the microprocessing technology for manufacturing 10-nm node devices of the next generation is a self-aligned quadruple patterning (SAQP) process involving repeating twice the SADP process of ArF lithography patterning. However, the SAQP process is believed very expensive in that formation of sidewall film by CVD and subsequent processing by dry etching must be repeated many times. The EUV lithography of wavelength 13.5 nm is capable of forming a pattern with a 10-nm size via a single exposure step, but suffers from low productivity because the laser power is yet low. As a way out of the deadlock of the miniaturization technology, the development of 3D devices such as vertically stacked flash memories typically BiCS is in progress, but this process is also expensive.

As compared with the line pattern, the hole pattern is difficult to reduce the feature size. The SADP process is applicable to the line pattern to reduce its pitch to half, but not applicable to the hole pattern which is a two-dimensional pattern. Rather than the method of forming a hole pattern by combining a dark-field mask with a positive resist material, the method of forming a hole pattern by combining a bright-field mask of dot pattern with a negative resist material is successful in forming a finer hole pattern because of a higher optical contrast. If a negative resist material improved enough to surpass the resolution of positive resist material is developed, it will become possible to form a fine hole pattern by combining it with the dot pattern mask.

Recently a highlight is put on the organic solvent development again. A positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such pattern forming process is described in Patent Document 1.

In forming a negative pattern of resist film, a bright-field pattern like a dot pattern is necessary at the mask pattern forming stage. In this case, the negative resist material has such advantages as a high throughput and minimized impact of backscattering on account of a reduced image area over the positive resist material. There is a need for a negative resist material having improved resolution.

The resist material for mask pattern formation must have dry etch resistance because the underlying is a metal film which is difficult to process such as Cr or MoSi. In the above-mentioned method of forming a negative pattern via organic solvent development of ArF resist composition, dry etch resistance is short because cyclic protective groups having dry etch resistance have been eliminated from the film that is left as the negative pattern. Thus, the method of forming a negative pattern via organic solvent development of resist film after deprotection is not viable.

Negative resist material of crosslink type suffers bridging between pattern features and pattern collapse due to swelling. A study is thus made on negative resist material of polarity change type rather than the crosslink type. Patent Document 2 discloses a negative resist composition utilizing the polarity change reaction that a hydroxycarboxylic structure cyclizes to form a lactone structure. Patent Document 3 describes a negative resist composition of polarity change type utilizing pinacol-pinacolone rearrangement.

For the purpose of improving etch resistance, on the other hand, styrene copolymers were first proposed. Later proposed are indene copolymers and acenaphthylene copolymers as described in Patent Documents 4 and 5. These copolymers intend to improve etch resistance by utilizing a high carbon density and a robust backbone framework of cycloolefin structure.

CITATION LIST

Patent Document 1: JP 4554665 (U.S. Pat. No. 8,530,143)

Patent Document 2: JP-A 2003-195502 (U.S. Pat. No. 6,800,423)

Patent Document 3: JP-A H07-239547

Patent Document 4: JP 3865048

Patent Document 5: JP-A 2006-169302

DISCLOSURE OF INVENTION

An object of the invention is to provide a negative resist composition which forms a pattern of satisfactory profile at a high resolution surpassing prior art negative resist compositions and with minimal edge roughness (LER, LWR) after exposure, especially a negative resist composition comprising a polymer which is an appropriate base resin for chemically amplified negative resist material, and a pattern forming process using the same.

Seeking for a negative resist material featuring a high sensitivity, high resolution and minimal edge roughness, the inventors have found that better results are obtained when a polymer comprising recurring units capable of forming a lactam ring under the action of acid is used as a base resin in a negative resist material, especially a chemically amplified negative resist material.

For the purpose of suppressing acid diffusion to improve dissolution contrast, it is effective to use a polymer comprising recurring units having the general formula (1), defined below, as a base resin in a negative resist material, especially a chemically amplified negative resist material. The resulting negative resist material, especially chemically amplified negative resist material has many advantages including a significantly high contrast of alkaline dissolution rate before and after exposure, acid diffusion suppressing effect, high resolution, and pattern formation of satisfactory profile and edge roughness after exposure, and is thus best suited as a micropatterning material for the fabrication of VLSI and photomasks.

The negative resist composition of the invention has a satisfactory effect of suppressing acid diffusion and a high resolution, lends itself to the lithography process, and forms a pattern of good profile and minimal edge roughness after exposure. Because of these advantages, the composition is readily implemented in practice and best suited as a VLSI-forming resist material and mask pattern forming material.

In one aspect, the invention provides a negative resist composition comprising a polymer comprising recurring units (a) of the general formula (1) and having a weight average molecular weight of 1,000 to 500,000 as base resin.

Herein R¹ is hydrogen or methyl, X is a single bond or —C(═O)—O—R⁴—, R² is a single bond or C₁-C₄ alkylene group, R³ is a linear C₂-C₈ alkylene group, R⁴ is a single bond or C₁-C₄ alkylene group, and a is in the range: 0<a≦1.0.

In a preferred embodiment, the polymer further comprises recurring units of at least one type selected from the group consisting of a vinylnaphthalene (b1), indene (b2), acenaphthylene (b3), chromone (b4), coumarin (b5), norbornadiene (b6), and vinylcarbazole (b7), as represented by the general formula (2).

Herein R⁵ is hydrogen or methyl, m is an integer of 0 to 2, n is an integer of 0 to 5, R¹¹⁰ to R¹¹⁶ are each independently hydrogen, C₁-C₃₀ alkyl, partially or entirely halo-substituted alkyl (the alkyl and halo-substituted alkyl optionally having an alkyl-substituted or unsubstituted hydroxyl or carboxyl group), hydroxyl, C₁-C₄ alkoxy, acyl, acyloxy, alkoxycarbonyl, C₆-C₁₀ aryl, halogen, or 1,1,1,3,3,3-hexafluoro-2-propanol group, Y is a single bond, —O—, —S—, —C(═O)—O—R⁶—, or —C(═O)—NH—R⁶—, R⁶ is a single bond or C₁-C₄ alkylene group, X⁰ is methylene, oxygen or sulfur atom; b1 to b7 are numbers in the range: 0≦b1<1.0, 0≦b2<1.0, 0≦b3<1.0, 0≦b4<1.0, 0≦b5<1.0, 0≦b6<1.0, 0≦b7<1.0, 0<b1+b2+b3+b4+b5+b6+b7<1.0, 0<a<1.0, and 0<a+b1+b2+b3+b4+b5+b6+b7≦1.0.

The resist composition may further comprise an organic solvent and an acid generator, the composition being a chemically amplified resist composition. The composition may further comprise a basic compound and/or a surfactant.

In another aspect, the invention provides a pattern forming process comprising the steps of applying the negative resist composition defined above onto a substrate, prebaking the composition to form a resist film, exposing the resist film to high-energy radiation, and developing in a developer.

In a preferred embodiment, the high-energy radiation is g-line of wavelength 430 nm, i-line of 365 nm, KrF excimer laser of 248 nm, electron beam (EB), or soft X-ray in a wavelength range of 3 to 15 nm. Typically, the developer is an alkaline developer.

The negative resist compositions, especially chemically amplified negative resist compositions are used not only in the lithography for semiconductor circuit formation, but also in the formation of mask circuit patterns, micro-machines, and thin-film magnetic head circuits.

Advantageous Effects of Invention

The negative resist composition of the invention is unlikely to swell in the developer and hence, to pattern collapse. A satisfactory effect of suppressing acid diffusion leads to a high resolution. The negative resist composition, typically chemically amplified negative resist composition is best suited as a micropatterning material by lithography processes using radiation or EB for the microfabrication of VLSI or photomasks.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. “Optional” or “optionally” means that the subsequently described event or circumstances may or may not occur, and that description includes instances where the event or circumstance occurs and instances where it does not. The notation (Cn—Cm) means a group containing from n to m carbon atoms per group. The term “film” is used interchangeably with “coating” or “layer.” The term “processable layer” is interchangeable with patternable layer and refers to a layer that can be processed such as by etching to form a pattern therein.

The abbreviations and acronyms have the following meaning.

PAG: photoacid generator

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure baking

TMAH: tetramethylammonium hydroxide

One embodiment of the invention is a negative resist composition comprising a polymer comprising recurring units (a) of the general formula (1) as base resin.

Herein R¹ is hydrogen or methyl, X is a single bond or —C(═O)—O—R⁴—, R² is a single bond or C₁-C₄ alkylene group, R³ is a linear C₂-C₈ alkylene group, R⁴ is a single bond or C₁-C₄ alkylene group, and a is a number in the range: 0<a≦1.0.

The recurring unit (a) cyclizes under the action of acid, to form a lactam ring as shown by the reaction scheme below. Prior to cyclization, the polymer has a high dissolution rate in alkaline developer because of the presence of a carboxyl group. After cyclization, a drastic drop of alkaline dissolution rate occurs because of the extinction of the carboxyl group. The resist composition of the invention is a negative resist composition adapted to change its alkaline dissolution rate via a change of polymer polarity without resorting to crosslinking reaction. The resist composition is characterized by a very high dissolution contrast.

The rate of cyclization reaction may be controlled by the length of alkylene group W. In case where the alkylene group R³ is propylene, a 5-membered ring is formed as illustrated above in the reaction scheme, and the reaction rate is the fastest. In case where the alkylene group R³ is ethylene, a 4-membered ring is formed, and in case where the alkylene group R³ is butylene, a 6-membered ring is formed, and in these cases, the reaction rate is slower than the 5-membered ring case. A higher rate of cyclization reaction gives a higher contrast whereas a lower rate leads to the advantage of storage stability. As the length of alkylene group R³, ethylene, propylene, butylene and pentylene are preferred.

The monomer from which the recurring unit (a) of formula (1) is derived may be obtained by reaction of aminostyrene with a halide having a carboxyl group as shown below. The carboxyl group may have been substituted, and in such a case, the substituent may be deprotected after monomer synthesis or polymerization.

Examples of the monomer from which the recurring unit (a) of formula (1) is derived are shown below.

Herein R¹ is as defined above.

In addition to the recurring units (a) of formula (1), the polymer as base resin may have further copolymerized therein recurring units of at least one type selected from recurring units (b1) to (b7) as represented by the general formula (2). A polymer having these units incorporated has an increased carbon density and hence, higher dry etch resistance.

Herein R⁵ is hydrogen or methyl, m is an integer of 0 to 2, and n is an integer of 0 to 5. R¹¹⁰ to R¹¹⁶ are each independently hydrogen, C₁-C₃₀ alkyl, partially or entirely halo-substituted alkyl (the alkyl and halo-substituted alkyl optionally having an alkyl-substituted or unsubstituted hydroxyl or carboxyl group), hydroxyl, C₁-C₄ alkoxy, acyl, acyloxy, alkoxycarbonyl, C₆-C₁₀ aryl, halogen, or 1,1,1,3,3,3-hexafluoro-2-propanol group. Y is a single bond, —O—, —S—, —C(═O)—O—R⁶—, or —C(═O)—NH—R⁶—, wherein R⁶ is a single bond or C₁-C₄ alkylene group. X⁰ is methylene, oxygen or sulfur atom; b1 to b7 are numbers in the range: 0≦b1<1.0, 0≦b2<1.0, 0≦b3<1.0, 0≦b4<1.0, 0≦b5<1.0, 0≦b6<1.0, 0≦b7<1.0, and 0≦b1+b2+b3+b4+b5+b6+b7<1.0.

Examples of the monomer from which recurring units (b1) are derived are shown below.

Herein R⁵ is as defined above, and R⁷ is hydrogen or C₁-C₄ alkyl.

Examples of the monomers from which recurring units (b2) to (b7) are derived are shown below.

While the polymer as base resin should comprise essentially recurring units (a) of formula (1) and optionally recurring units (b1) to (b7) copolymerized therewith as alluded to above, it may have further copolymerized therein recurring units (c) having an adhesive group. The adhesive group is selected from among hydroxyl, carboxyl, lactone ring, carbonate, thiocarbonate, carbonyl, cyclic acetal, ether, ester, sulfonic acid ester, cyano, amide, —O—C(═O)-G- (wherein G is sulfur or NH), and acid anhydride groups.

Shown below are examples of the monomer from which the recurring units (c) having an adhesive group selected from among hydroxyl, carboxyl, lactone ring, carbonate, thiocarbonate, carbonyl, cyclic acetal, ether, ester, sulfonic acid ester, cyano, amide, —O—C(═O)-G- (wherein G is sulfur or NH) and acid anhydride groups are derived.

In the case of a monomer having a hydroxyl group, the hydroxyl group may be replaced by an acetal group susceptible to deprotection with acid, typically ethoxyethoxy, prior to polymerization, and the polymerization be followed by deprotection with weak acid and water. Alternatively, the hydroxyl group may be replaced by an acetyl, formyl, pivaloyl or similar group prior to polymerization, and the polymerization be followed by alkaline hydrolysis.

In a more preferred embodiment, recurring units (d1), (d2) or (d3) having a sulfonium salt as represented by the following general formula (3) may be copolymerized. It is noted that JP-A 2006-045311 discloses a sulfonium or iodonium salt having polymerizable olefin capable of generating a specific sulfonic acid; and JP-A 2006-178317 discloses a sulfonium salt having sulfonic acid directly attached to the main chain.

Herein R²⁰, R²⁴, and R²⁵ each are hydrogen or methyl. R²¹ is a single bond, phenylene, —O—R—, or —C(═O)—Y₀—R—. Y₀ is oxygen or NH. R is a straight, branched or cyclic C₁-C₆ alkylene group, alkenylene group or phenylene group, which may contain a carbonyl (—CO—), ester (—COO—), ether (—O—), or hydroxyl moiety. R²², R²³, R²⁵, R²⁶, R²⁷, R²⁸, R³⁰, and R³¹ are each independently a straight, branched or cyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester or ether moiety, a C₆-C₁₂ aryl group, a C₇-C₂₀ aralkyl group, or a thiophenyl group. Z₀ is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R³²—, or —C(═O)—Z₁—R³²—, wherein Z₁ is oxygen or NH, and R³² is a straight, branched or cyclic C₁-C₆ alkylene group, alkenylene group or phenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety. M is a non-nucleophilic counter ion.

Binding an acid generator to the polymer backbone is effective for reducing acid diffusion and preventing the resolution from lowering due to blur by acid diffusion. Additionally, edge roughness (LER, LWR) is improved because the acid generator is uniformly dispersed.

Examples of the non-nucleophilic counter ion represented by M⁻ include halide ions such as chloride and bromide ions; fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such as mesylate and butanesulfonate; imidates such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsulfonyl)imide; methidates such as tris(trifluoromethylsulfonyl)methide and tris(perfluoroethylsulfonyl)methide.

Other non-nucleophilic counter ions include sulfonates having fluorine substituted at α-position as represented by the general formula (K-1) and sulfonates having fluorine substituted at α- and β-positions as represented by the general formula (K-2).

In formula (K-1), R¹⁰² is hydrogen, or a straight, branched or cyclic C₁-C₂₀ alkyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl group, which may have an ether, ester, carbonyl moiety, lactone ring or fluorine. In formula (K-2), R¹⁰³ is hydrogen, or a straight, branched or cyclic C₁-C₃₀ alkyl or acyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl or aryloxy group, which may have an ether, ester, carbonyl moiety or lactone ring.

The polymer defined herein may be synthesized by any desired methods, for example, by dissolving suitable monomers selected from the monomers to form the recurring units (a) to (d) in an organic solvent, adding a radical polymerization initiator thereto, and effecting heat polymerization. Examples of the organic solvent which can be used for polymerization include toluene, benzene, tetrahydrofuran, diethyl ether, dioxane, cyclohexane, cyclopentane, methyl ethyl ketone, and α-butyrolactone. Examples of the polymerization initiator used herein include 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis(2,4-dimethyl-valeronitrile), dimethyl 2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide. Preferably the system is heated at 50 to 80° C. for polymerization to take place. The reaction time is 2 to 100 hours, preferably 5 to 20 hours.

In order to prevent the recurring unit (a) from cyclization by the heat during polymerization, a basic substance may be added to the polymerization system. The basic substance added herein is preferably a weakly basic compound, examples of which include aromatic amine compounds and amide compounds such as pyridine, dimethylaniline and quinoline.

When a hydroxyl-containing monomer such as hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, an alternative method is possible. Specifically, acetoxystyrene or acetoxyvinylnaphthalene is used instead of hydroxystyrene or hydroxyvinylnaphthalene, and after polymerization, the acetoxy group is deprotected by alkaline hydrolysis as mentioned above, for thereby converting the polymer product to polyhydroxystyrene or hydroxypolyvinylnaphthalene. For alkaline hydrolysis, a base such as aqueous ammonia or triethylamine may be used. The reaction temperature is −20° C. to 100° C., preferably 0° C. to 60° C., and the reaction time is 0.2 to 100 hours, preferably 0.5 to 20 hours.

In the (co)polymer, recurring units (a) to (d) may be incorporated in the following molar fraction: 0<a≦1.0, 0≦b1<1.0, 0≦b2<1.0, 0≦b3<1.0, 0≦b4<1.0, 0≦b5<1.0, 0≦b6<1.0, 0≦b7<1.0, 0≦b1+b2+b3+b4+b5+b6+b7<1.0, 0≦c<1.0, 0≦d1≦0.5, 0≦d2≦0.5, 0≦d3≦0.5, and 0≦d1+d2+d3≦0.5; preferably 0.05≦a≦1.0, 0≦b1≦0.95, 0≦b2≦0.95, 0≦b3≦0.95, 0≦b4≦0.95, 0≦b5≦0.95, 0≦b6≦0.95, 0≦b7≦0.95, 0≦b1+b2+b3+b4+b5+b6+b7≦0.95, 0≦c≦0.9, 0≦d1≦0.4, 0≦d2≦0.4, 0≦d3≦0.4, and 0≦d1+d2+d3≦0.4;

more preferably 0.1≦a≦1.0, 0≦b1≦0.9, 0≦b2≦0.9, 0≦b3≦0.9, 0≦b4≦0.9, 0≦b5≦0.9, 0≦b6≦0.9, 0≦b7≦0.9, 0≦b1+b2+b3+b4+b5+b6+b7≦0.9, 0≦c≦0.8, 0≦d1≦0.35, 0≦d2≦0.35, 0≦d3≦0.35, and 0≦d1+d2+d3≦0.35. The more preferred range is a<1.0 and 0<b1+b2+b3+b4+b5+b6+b7.

The polymer for use in the negative resist composition should have a weight average molecular weight (Mw) in the range of 1,000 to 500,000, and preferably 2,000 to 30,000, as measured by gel permeation chromatography (GPC) versus polystyrene standards using tetrahydrofuran as a solvent. With too low a Mw, the resist composition becomes less heat resistant. A polymer with too high a Mw loses alkaline solubility and gives rise to a footing phenomenon after pattern formation.

If a multi-component polymer has a wide molecular weight distribution or dispersity (Mw/Mn), which indicates the presence of lower and higher molecular weight polymer fractions, there is a possibility that foreign matter is left on the pattern or the pattern profile is degraded. The influences of molecular weight and dispersity become stronger as the pattern rule becomes finer. Therefore, the multi-component copolymer should preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide a resist composition suitable for micropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ in compositional ratio, molecular weight or dispersity is acceptable as well as a blend of an inventive polymer and a polymer free of recurring units (a) of formula (1).

The polymer is advantageously used as a base resin in a negative resist composition, typically chemically amplified negative resist composition. Specifically, the polymer is used as a base resin and combined with any desired components including an organic solvent, acid generator, dissolution regulator, basic compound, and surfactant to formulate a negative resist composition. In the exposed region, the dissolution rate of the polymer in developer is accelerated by catalytic reaction, that is, a negative resist composition with a very high sensitivity is obtained. This negative resist composition forms a resist film having a high dissolution contrast, resolution, exposure latitude, and process adaptability, and providing a good pattern profile after exposure, yet better etch resistance, and minimal proximity bias because of controlled acid diffusion. Because of these advantages, the composition is readily implemented in practice and best suited as a VLSI-forming resist material and mask pattern forming material. Particularly when an acid generator is added to the composition to formulate a chemically amplified negative resist composition capable of utilizing acid-catalyzed reaction, the composition has a higher sensitivity and is further improved in the properties described above.

A crosslinker may be added to the negative resist composition. Suitable crosslinkers which can be used herein include melamine compounds, guanamine compounds, glycoluril compounds and urea compounds having substituted thereon at least one group selected from among methylol, alkoxymethyl and acyloxymethyl groups, epoxy compounds, isocyanate compounds, azide compounds, and compounds having a double bond such as an alkenyl ether group. These compounds may be used as an additive or introduced into a polymer side chain as a pendant. Hydroxy-containing compounds may also be used as the crosslinker.

Of the foregoing crosslinkers, examples of suitable epoxy compounds include tris(2,3-epoxypropyl) isocyanurate, trimethylolmethane triglycidyl ether, trimethylolpropane triglycidyl ether, and triethylolethane triglycidyl ether. Examples of the melamine compound include hexamethylol melamine, hexamethoxymethyl melamine, hexamethylol melamine compounds having 1 to 6 methylol groups methoxymethylated and mixtures thereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine, hexamethylol melamine compounds having 1 to 6 methylol groups acyloxymethylated and mixtures thereof. Examples of the guanamine compound include tetramethylol guanamine, tetramethoxymethyl guanamine, tetramethylol guanamine compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, tetramethoxyethyl guanamine, tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4 methylol groups acyloxymethylated and mixtures thereof. Examples of the glycoluril compound include tetramethylol glycoluril, tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylol glycoluril compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, tetramethylol glycoluril compounds having 1 to 4 methylol groups acyloxymethylated and mixtures thereof. Examples of the urea compound include tetramethylol urea, tetramethoxymethyl urea, tetramethylol urea compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, and tetramethoxyethyl urea.

Suitable isocyanate compounds include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate and cyclohexane diisocyanate. Suitable azide compounds include 1,1′-biphenyl-4,4′-bisazide, 4,4′-methylidenebisazide, and 4,4′-oxybisazide. Examples of the alkenyl ether group-containing compound include ethylene glycol divinyl ether, triethylene glycol divinyl ether, 1,2-propanediol divinyl ether, 1,4-butanediol divinyl ether, tetramethylene glycol divinyl ether, neopentyl glycol divinyl ether, trimethylol propane trivinyl ether, hexanediol divinyl ether, 1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitol pentavinyl ether, and trimethylol propane trivinyl ether.

The crosslinker may be blended in an amount of 0 to 50 parts, preferably 5 to 50 parts, and more preferably 10 to 30 parts by weight per 100 parts by weight of the base resin. At least 5 parts of the crosslinker achieves a sufficient improvement in resolution. As long as the amount of the crosslinker is not more than 50 parts, there is a minimized risk that resolution is reduced as a result of pattern features merging together. The crosslinkers may be used alone or in admixture.

Addition of a basic compound may be effective in suppressing the diffusion rate of acid in the resist film, achieving a further improvement in resolution. Addition of a surfactant may improve or control the coating characteristics of the resist composition.

The resist composition may include an acid generator in order for the composition to function as a chemically amplified negative resist composition. Typical of the acid generator used herein is a photoacid generator (PAG) capable of generating an acid in response to actinic light or radiation. It is any compound capable of generating an acid upon exposure to high-energy radiation. Suitable PAGs include sulfonium salts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. The acid generators may be used alone or in admixture of two or more. Exemplary acid generators are described in JP-A 2008-111103, paragraphs [0122] to [0142] (U.S. Pat. No. 7,537,880). In the embodiment wherein a polymer having recurring units (d1), (d2) or (d3) copolymerized therein is used as the base resin, the PAG may be omitted.

As alluded to above, an organic solvent, basic compound, dissolution regulator, surfactant, and/or acetylene alcohol may be added to the resist composition. Examples of the organic solvent used herein are described in JP-A 2008-111103, paragraphs [0144] to [0145] (U.S. Pat. No. 7,537,880), exemplary basic compounds in paragraphs [0146] to [0164], and exemplary surfactants in paragraphs [0165] to [0166]. Exemplary dissolution regulators are described in JP-A 2008-122932 (US 2008090172), paragraphs [0155] to [0178], and exemplary acetylene alcohols in paragraphs [0179] to [0182]. Also useful are quenchers of polymer type as described in JP-A 2008-239918. The polymeric quencher segregates at the resist surface after coating and thus enhances the rectangularity of resist pattern. When a protective film is applied as is often the case in the immersion lithography, the polymeric quencher is also effective for preventing any film thickness loss of resist pattern or rounding of pattern top.

An appropriate amount of the acid generator used is 0.01 to 100 parts, and preferably 0.1 to 80 parts. An appropriate amount of the organic solvent used is 50 to 10,000 parts, especially 100 to 5,000 parts. The dissolution regulator may be blended in an amount of 0 to 50 parts, preferably 0 to 40 parts, the basic compound in an amount of 0 to 100 parts, preferably 0.001 to 50 parts, and the surfactant in an amount of 0 to 10 parts, preferably 0.0001 to 5 parts. All amounts are expressed in parts by weight relative to 100 parts by weight of the base resin.

Process

The negative resist composition, typically chemically amplified negative resist composition comprising a polymer comprising recurring units (a) of formula (1), an acid generator, and a basic compound in an organic solvent is used in the fabrication of various integrated circuits. Pattern formation using the resist composition may be performed by well-known lithography processes. The process generally involves coating of the resist composition on a substrate, prebake, exposure to high-energy radiation, and development in a developer for thereby forming a pattern on the substrate. If necessary, any additional steps may be added.

For instance, the negative resist composition is applied onto a substrate on which an integrated circuit is to be formed (e.g., Si, SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating) or a substrate on which a mask circuit is to be formed (e.g., Cr, CrO, CrON or MoSi) by a suitable coating technique such as spin coating, roll coating, flow coating, dip coating, spray coating or doctor coating. The coating is prebaked on a hot plate at a temperature of 60 to 150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30 seconds to 20 minutes. The resulting resist film is generally 0.1 to 2.0 μm thick. If desired, a protective film may be formed on the resist film. The protective film is preferably formed of an alkaline developer-soluble composition so that both formation of a resist pattern and stripping of the protective film may be achieved during development. The protective film has the functions of restraining outgassing from the resist film, filtering or cutting off out-of-band (00B) light having a wavelength of 140 to 300 nm emitted by the EUV laser (other than 13.5 nm), and preventing the resist film from assuming T-top profile or from losing its thickness under environmental impacts.

The resist film is then exposed to a desired pattern of high-energy radiation such as UV, deep-UV, EB, x-ray, excimer laser light, γ-ray, synchrotron radiation or EUV (soft x-ray), directly or through a mask. The exposure dose is preferably about 1 to 200 mJ/cm², more preferably about 10 to 100 mJ/cm², or 0.1 to 100 μC/cm², more preferably 0.5 to 50 οC/cm². The resist film is further baked (PEB) on a hot plate at 60 to 150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30 seconds to 20 minutes.

Thereafter the resist film is developed in a developer in the form of an aqueous alkaline solution for 3 seconds to 3 minutes, preferably 5 seconds to 2 minutes by conventional techniques such as dip, puddle or spray techniques. Suitable developers include 0.1 to 10 wt %, preferably 2 to 5 wt % aqueous solutions of tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH). The exposed region of resist film is insolubilized whereas the unexposed region of resist film is dissolved in the developer. In this way, the desired negative pattern is formed on the substrate. It is appreciated that the resist composition of the invention is best suited for micro-patterning using such high-energy radiation as EB, EUV (soft x-ray), x-ray, α-ray and synchrotron radiation among others.

Although TMAH aqueous solution is generally used as the developer, TEAH, TPAH and TBAH having a longer alkyl chain are effective in inhibiting the resist film from being swollen during development and thus preventing pattern collapse. JP 3429592 describes an example using an aqueous TBAH solution for the development of a polymer comprising recurring units having an alicyclic structure such as adamantane methacrylate and recurring units having an acid labile group such as tert-butyl methacrylate, the polymer being water repellent due to the absence of hydrophilic groups.

The TMAH developer is most often used as 2.38 wt % aqueous solution, which corresponds to 0.26N. The TEAH, TPAH, and TBAH aqueous solutions should preferably have an equivalent normality. The concentration of TEAH, TPAH, and TBAH that corresponds to 0.26N is 3.84 wt %, 5.31 wt %, and 6.78 wt %, respectively.

When a pattern with a line size of 32 nm or less is resolved by the EB and EUV lithography, there arises a phenomenon that lines become wavy, lines merge together, and merged lines collapse. It is believed that this phenomenon occurs because lines are swollen in the developer and the thus expanded lines merge together. Since the swollen lines containing liquid developer are as soft as sponge, they readily collapse under the stress of rinsing. For this reason, the developer using a long-chain alkyl developing agent is effective for preventing film swell and hence, pattern collapse.

At the end of development, the resist film is rinsed. Although water is most often used as the rinsing liquid, use may also be made of a rinse liquid having a surfactant added thereto for the purpose of preventing pattern collapse or a rinse liquid having carbonic acid or acidic substance added thereto for the purpose of preventing blob defect formation.

EXAMPLE

Examples of the invention are given below by way of illustration and not by way of limitation. For all polymers, Mw and Mn are determined versus polystyrene standards by GPC using tetrahydrofuran solvent. All parts are by weight (pbw).

As used in Synthesis Examples, Monomers 1 to 4, Adhesive Monomers 1 and 2, and PAG Monomer 1 are identified below.

-   Adhesive Monomer 1: 2-oxo-1,3-benzoxathiol-5-yl methacrylate -   Adhesive Monomer 2: 2-oxo-2,3-dihydrobenzoxazol-5-yl methacrylate

-   PAG Monomer 1: triphenylsulfonium     1,1,3,3,3-pentafluoro-2-methacryloyloxypropane-1-sulfonate

Synthesis Example 1

A 2-L flask was charged with 4.1 g of Monomer 1, 6.0 g of 4-hydroxystyrene, 3.1 g of styrene, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of azobisisobutyronitrile (AIBN) was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was collected by filtration and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 1: 4-hydroxystyrene:styrene=0.20:0.50:0.30     -   Mw=6,600     -   Mw/Mn=1.76     -   This polymer is designated Polymer 1.

Synthesis Example 2

A 2-L flask was charged with 4.1 g of Monomer 1, 7.2 g of 4-hydroxystyrene, 2.9 g of indene, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 1: 4-hydroxystyrene:indene=0.20:0.60:0.20     -   Mw=6,100     -   Mw/Mn=1.61     -   This polymer is designated Polymer 2.

Synthesis Example 3

A 2-L flask was charged with 4.1 g of Monomer 1, 7.2 g of 4-hydroxystyrene, 3.7 g of coumarin, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 1: 4-hydroxystyrene:coumarin=0.20:0.60:0.20     -   Mw=6,300     -   Mw/Mn=1.69     -   This polymer is designated Polymer 3.

Synthesis Example 4

A 2-L flask was charged with 4.1 g of Monomer 1, 7.2 g of 4-hydroxystyrene, 3.7 g of chromone, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 1: 4-hydroxystyrene:chromone=0.20:0.60:0.20     -   Mw=6,100     -   Mw/Mn=1.67     -   This polymer is designated Polymer 4.

Synthesis Example 5

A 2-L flask was charged with 4.1 g of Monomer 1, 7.2 g of 4-hydroxystyrene, 3.7 g of methyl 2,5-norbornadiene-2-carboxylate, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 1: 4-hydroxystyrene:methyl         2,5-norbornadiene-2-carboxylate=0.20:0.60:0.20     -   Mw=5,100     -   Mw/Mn=1.69     -   This polymer is designated Polymer 5.

Synthesis Example 6

A 2-L flask was charged with 4.1 g of Monomer 1, 7.2 g of 4-hydroxystyrene, 3.9 g of N-vinylcarbazole, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 1: 4-hydroxystyrene:N-vinylcarbazole=0.20:0.60:0.20     -   Mw=5,600     -   Mw/Mn=1.77     -   This polymer is designated Polymer 6.

Synthesis Example 7

A 2-L flask was charged with 23.3 g of Monomer 3, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Polymer compositional ratio (molar ratio)     -   Monomer 3=1.00     -   Mw=7,100     -   Mw/Mn=1.71     -   This polymer is designated Polymer 7.

Synthesis Example 8

A 2-L flask was charged with 4.4 g of Monomer 2, 13.5 g of 4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)styrene, 3.1 g of 1-vinylnaphthalene, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 2:         4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)-styrene:1-vinylnaphthalene=0.20:0.50:0.30     -   Mw=6,600     -   Mw/Mn=1.76     -   This polymer is designated Polymer 8.

Synthesis Example 9

A 2-L flask was charged with 6.6 g of Monomer 2, 20 g of fluorescein methacrylate, 3 g of acenaphthylene, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 2: fluorescein         methacrylate:acenaphthylene=0.30:0.50:0.20     -   Mw=6,500     -   Mw/Mn=1.86     -   This polymer is designated Polymer 9.

Synthesis Example 10

A 2-L flask was charged with 6.6 g of Monomer 2, 4.1 g of 4-hydroxy-3,5-dimethylphenyl methacrylate, 11.8 g of Adhesive Monomer 1, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and vacuum dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 2: 4-hydroxy-3,5-dimethylphenyl methacrylate:Adhesive         Monomer 1=0.30:0.20:0.50     -   Mw=7,000     -   Mw/Mn=1.79     -   This polymer is designated Polymer 10.

Synthesis Example 11

A 2-L flask was charged with 6.6 g of Monomer 2, 3.6 g of 4-hydroxyphenyl methacrylate, 6.6 g of Adhesive Monomer 2, 5.6 g of PAG Monomer 1, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and vacuum dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 2: 4-hydroxyphenyl methacrylate:Adhesive Monomer 2: PAG         Monomer 1=0.30:0.30:0.30:0.10     -   Mw=7,900     -   Mw/Mn=1.70     -   This polymer is designated Polymer 11.

Synthesis Example 12

A 2-L flask was charged with 6.6 g of Monomer 4, 6.8 g of 5-hydroxynaphthalen-1-yl methacrylate, 6.7 g of 3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.6 g of PAG Monomer 1, 1 g of pyridine, and 40 g of tetrahydrofuran as solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN was added. The reactor was heated at 60° C., whereupon reaction ran for 15 hours. The reaction solution was poured into 1 L of isopropyl alcohol for precipitation. The resulting white solid was filtered and vacuum dried at 60° C., yielding a white polymer. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   Monomer 4: 5-hydroxynaphthalen-1-yl         methacrylate:3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl         methacrylate:PAG Monomer 1=0.30:0.30:0.30:0.10     -   Mw=7,800     -   Mw/Mn=1.77

This polymer is designated Polymer 12.

Comparative Synthesis Example 1

A binary polymer was synthesized by the same procedure as in the above Synthesis Examples. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)     -   hydroxystyrene:styrene=0.70:0.30     -   Mw=4,500     -   Mw/Mn=1.55     -   This polymer is designated Comparative Polymer 1.

Comparative Synthesis Example 2

A binary polymer was synthesized by the same procedure as in the above Synthesis Examples. The polymer was analyzed by ¹³C- and ¹H-NMR and GPC, with the results shown below.

-   -   Copolymer compositional ratio (molar ratio)         hydroxystyrene:acenaphthylene=0.80:0.20     -   Mw=5,900     -   Mw/Mn=1.59     -   This polymer is designated Comparative Polymer 2.

Examples and Comparative Examples

A negative resist composition was prepared by dissolving each polymer (Polymers 1 to 12) and other components in a solvent in accordance with the recipe shown in Table 1, and filtering through a filter with a pore size of 0.2 μm. The solvent contained 100 ppm of surfactant FC-4430 (3M-Sumitomo Co., Ltd.).

The components in Table 1 are identified below.

-   Polymers 1 to 12: Polymers obtained in Synthesis Examples 1 to 12 -   Comparative Polymers 1 and 2:     -   Polymers obtained in Comparative Synthesis Examples 1 and 2 -   Organic solvent: propylene glycol monomethyl ether acetate (PGMEA)     -   propylene glycol monomethyl ether (PGME)     -   cyclohexanone (CyH)     -   cyclopentanone (CyP) -   Acid generator: PAG1 of the structural formula below -   Crosslinker: CR1 of the structural formula below -   Basic compound: Amine 1 of the structural formula below

EB Writing Test

A silicon substrate having a diameter of 6 inches was vapor primed with hexamethyldisilazane (HMDS). Using a coater/developer system Clean Track Mark 5 (Tokyo Electron Ltd.), the negative resist composition was spin coated onto the substrate and pre-baked on a hot plate at 110° C. for 60 seconds to form a resist film of 100 nm thick. Using a system HL-800D (Hitachi Ltd.) at a HV voltage of 50 kV, the resist film was exposed imagewise to EB in a vacuum chamber.

Using Clean Track Mark 5, immediately after the imagewise exposure, the resist film was baked (PEB) on a hot plate at the temperature shown in Table 1 for 60 seconds and puddle developed in a 2.38 wt % TMAH aqueous solution for 30 seconds to form a negative pattern.

The resulting resist pattern was evaluated as follows.

Sensitivity is the exposure dose that provides a 1:1 resolution of a 100-nm line-and-space pattern. Resolution is a minimum size at the optimum dose. The 100-nm L/S pattern was measured for edge roughness (LWR) under SEM. The sensitivity and resolution on EB lithography are shown in Table 1 together with the formulation of resist composition.

TABLE 1 Acid generator/ Basic Organic PEB Polymer crosslinker compound solvent temp. Sensitivity Resolution LWR (pbw) (pbw) (pbw) (pbw) (° C.) (μC/cm²) (nm) (nm) Example 1 Polymer 1 PAG1 Amine 1 PGMEA (1,500) 90 26.6 75 6.7 (100) (15) (1.0) CyH (200) 2 Polymer 2 PAG1 (15) Amine 1 PGMEA (1,500) 85 33.6 75 6.1 (100) CR1 (5) (1.0) CyH (200) 3 Polymer 3 PAG1 Amine 1 PGMEA (1,500) 95 27.3 75 6.4 (100) (15) (1.0) CyH (200) 4 Polymer 4 PAG1 Amine 1 PGMEA (1,500) 90 26.0 75 5.8 (100) (15) (1.0) CyH (200) 5 Polymer 5 PAG1 Amine 1 PGMEA (1,500) 95 26.3 75 6.4 (100) (15) (1.0) CyH (200) 6 Polymer 6 PAG1 Amine 1 PGMEA (1,500) 95 28.1 75 6.6 (100) (15) (1.0) CyH (200) 7 Polymer 7 PAG1 Amine 1 PGMEA (1,500) 90 26.3 85 7.3 (100) (15) (1.0) CyH (200) 8 Polymer 8 PAG1 Amine 1 PGMEA (1,500) 90 26.2 75 5.0 (100) (15) (1.0) CyH (200) 9 Polymer 9 PAG1 Amine 1 PGMEA (1,500) 95 23.3 75 5.7 (100) (15) (1.0) CyH (200) 10 Polymer 10 PAG1 Amine 1 PGMEA (1,500) 90 24.8 75 5.5 (100) (15) (1.0) CyH (200) 11 Polymer 11 — Amine 1 PGMEA (300) 100 31.3 70 4.9 (100) (1.0) CyH (1,450) CyP (250) 12 Polymer 12 — Amine 1 PGMEA (500) 100 33.6 70 4.5 (100) (1.0) CyH (1,450) PGME (50) Comparative 1 Comparative PAG1(15) Amine 1 PGMEA (1,500) 90 26.5 90 8.9 Example Polymer 1 CR1 (10) (1.0) CyH (200) (100) 2 Comparative PAG1 (15) Amine 1 PGMEA (1,500) 90 33.6 90 9.9 Polymer 2 CR1 (10) (1.0) CyH (200) (100)

As seen from Table 1, the negative resist composition within the scope of the invention meets satisfactory resolution, sensitivity and edge roughness. Using a copolymer having an acid generator copolymerized therein, the resolution and edge roughness are significantly improved.

Japanese Patent Application No. 2013-245671 is incorporated herein by reference.

Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims. 

1. A negative resist composition comprising a polymer comprising recurring units (a) of the general formula (1) and having a weight average molecular weight of 1,000 to 500,000 as base resin,

wherein R¹ is hydrogen or methyl, X is a single bond or —C(═O)—O—R⁴—, R² is a single bond or C₁-C₄ alkylene group, R³ is a linear C₂-C₈ alkylene group, R⁴ is a single bond or C₁-C₄ alkylene group, and a is in the range: 0<a≦1.0.
 2. The negative resist composition of claim 1 wherein the polymer further comprises recurring units of at least one type selected from the group consisting of a vinylnaphthalene (b1), indene (b2), acenaphthylene (b3), chromone (b4), coumarin (b5), norbornadiene (b6), and vinylcarbazole (b7), as represented by the general formula (2):

wherein R⁵ is hydrogen or methyl, m is an integer of 0 to 2, n is an integer of 0 to 5, R¹¹⁰ to R¹¹⁶ are each independently hydrogen, C₁-C₃₀ alkyl, partially or entirely halo-substituted alkyl (the alkyl and halo-substituted alkyl optionally having an alkyl-substituted or unsubstituted hydroxyl or carboxyl group), hydroxyl, C₁-C₄ alkoxy, acyl, acyloxy, alkoxycarbonyl, C₆-C₁₀ aryl, halogen, or 1,1,1,3,3,3-hexafluoro-2-propanol group, Y is a single bond, —O—, —S—, —C(═O)—O—R⁶—, or —C(═O)—NH—R⁶—, R⁶ is a single bond or C₁-C₄ alkylene group, X⁰ is methylene, oxygen or sulfur atom; b1 to b7 are numbers in the range: 0≦b1<1.0, 0≦b2<1.0, 0≦b3<1.0, 0≦b4<1.0, 0≦b5<1.0, 0≦b6<1.0, 0≦b7<1.0, 0<b1+b2+b3+b4+b5+b6+b7<1.0, 0<a<1.0, and 0<a+b1+b2+b3+b4+b5+b6+b7≦1.0.
 3. The negative resist composition of claim 1, further comprising an organic solvent and an acid generator, the composition being a chemically amplified resist composition.
 4. The negative resist composition of claim 1, further comprising a basic compound and/or a surfactant.
 5. A pattern forming process comprising the steps of applying the negative resist composition of claim 1 onto a substrate, prebaking the composition to form a resist film, exposing the resist film to high-energy radiation, and developing in a developer.
 6. The pattern forming process of claim 5 wherein the high-energy radiation is g-line of wavelength 430 nm, i-line of 365 nm, KrF excimer laser of 248 nm, EB, or soft X-ray in a wavelength range of 3 to 15 nm.
 7. The pattern forming process of claim 5 wherein the developer is an alkaline developer. 